Shell Programming and Scripting

#!/bin/bash
 
IFS="|"
 
set -- main
 
while [ "$#" -gt 0 ]
do
        case "$1" in    # Look up the right options for the menu
        main)           OPTIONS="Do maintenance|Look at logs|Look at Processes|Q" ;;
        submenu1)       OPTIONS="A|B|C|Q"       ;;
        submenu2)       OPTIONS="D|E|F|Q"       ;;
        submenu3)       OPTIONS="X|Y|Z|Q"       ;;
        esac
 
        PS3=$'\n'"$1 menu: "    # Special variable controlling select prompt
 
        # Print menu, get reply
        select X in $OPTIONS
        do
                [ -z "$X" ] || break
        done
 
        # We treat Q specially, it returns to the previous menu.
        if [ "$X" = "Q" ]
        then
                shift           # Return to previous menu
                continue        # Go to top of loop
        fi
 
        case "$1" in
        main)
                case "$X" in
                Do maintenance)    set -- submenu1 "$*"    ;;
                Look at logs)    set -- submenu2 "$*"    ;;
                Look at Processes)    set -- submenu3 "$*"    ;;
                esac
                ;;
 
        submenu1)
                case "$X" in
                A)     # Switch to submenu2 by removing submenu1 before adding
                        shift
                        set -- submenu2 "$*"
                        ;;
                B)      ;;
                C)      ;;
                esac
                ;;
 
        submenu2)
                case "$X" in
                A)      ;;
                B)      ;;
                C)      ;;
                esac
                ;;
 
        submenu3)
                case "$X" in
                A)      ;;
                B)      ;;
                C)      ;;
                esac
                ;;
 
        *)      echo "Unknown menu $1, removing"
                shift
                ;;
        esac
done
 
echo "Menu list is empty, quitting" >&2